MQ-136 hydrogen sulfide sensor with ESP32

Supply 5 V Bus ANALOG Measures hydrogen sulfide

Pins and ESP32 wiring

Pin	Role	ESP32 pin	Notes
VCC	Power	VIN	Needs 5 V for the heater (about 150 mA): use VIN
GND	Ground	GND
DO	Output (the part drives it)	D25	Threshold output. Its HIGH level is 5 V: use a voltage divider
AO	Analog output	D34	Can reach 5 V: use a voltage divider before the ADC

Suggested wiring for the 30-pin ESP32 DevKit, avoiding flash, input-only and strapping pins. BoardPilot checks it for you as you wire.

This module is sold for 5 V. Its outputs may be 5 V: use a level shifter or a voltage divider on ESP32 inputs.

void setup() { Serial.begin(115200); }

void loop() {
  int mv = analogReadMilliVolts(34);  // AO on GPIO 34
  Serial.println(mv);
  delay(200);
}

Winsen MQ136 datasheet, Sensitive to hydrogen sulfide (H2S)
Winsen MQ136 datasheet, Heater 5 V; needs a burn-in / warm-up time before readings are stable

Part data: CC BY 4.0, free to reuse with credit to BoardPilot.